1. Field of the Invention
The present invention relates to a penetration inhibitor, a method for preventing penetration of solvent ink into a print medium, solvent ink for an inkjet printer, and a method for producing solvent ink for an inkjet printer.
2. Discussion of the Background
Inkjet printing using such a solvent ink is widely used in printing for signs such as advertising displays and large-sized posters. Generally, solvent ink includes organic solvent (for example, a glycol ether compound or cyclohexanone) as a main component and further includes a colorant such as dye or pigment and a binder resin.
In the inkjet printing using the solvent ink, a printed matter is obtained in the following manner. First, the solvent ink is ejected from an inkjet head and is deposited on a print medium to form an image. The solvent in the solvent ink deposited on the print medium is absorbed in the print medium or removed from the printed surface by heating the print medium. Consequently, dried ink adheres tightly to the printed surface to form an ink coating, thereby obtaining the printed matter.
As print media used for the inkjet printing using the solvent ink, PVC sheets and tarpaulins having relatively high solvent-absorption property have been typically used. Recently, in addition to these print media, print media having hydrophilic porous print surface such as ink-jet print paper and offset printing plate member are also used for the inkjet printing using the solvent ink.
As the solvent ink used in the inkjet printing, for example, Japanese Unexamined Patent Application Publication No. 2001-311023 discloses a solvent ink containing resin particles, Japanese Unexamined Patent Application Publication No. 2004-224910 discloses a solvent ink containing hydrophobic polymer of which glass transition temperature (Tg) is 40° C. or more, Japanese Unexamined Patent Application Publication Nos. JP-A-6-240192, JP-A-10-140060 and JP-A-10-195356 disclose solvent inks containing predetermined resins. The contents of these publications are incorporated by reference in their entirety.
However, the solvent inks disclosed in these publications have the following problems. That is, there is a problem that ink bleed easily occurs in the obtained image when the aforementioned conventional solvent ink is used to perform inkjet printing onto a print medium having a hydrophilic porous print surface to be printed on because such print medium has low solvent absorbency and the ink thus penetrates into the print medium.
When inkjet printing is performed to an offset printing plate member by using the aforementioned conventional solvent ink, the ink penetrates into the print medium so as to reduce the amount of ink coating formed on the printed surface. Accordingly, the ink coating on the obtained offset plate has insufficient water resistance and insufficient water repellency. When this offset plate with the insufficient amount of ink coating is used for the offset printing, the adhesion of ink for offset printing relative to the offset plate is poor, that is, there is a problem that sufficient plate life is not obtained.
For the purpose of achieving the aforementioned object, the present invention provides a penetration inhibitor, to be added to an inkjet solvent ink for preventing the penetration of the solvent ink into a print medium, comprising a rosin-series resin of which weight-average molecular weight is from 16,000 to 50,000.
Using the penetration inhibitor of the present invention, there is provided a solvent ink which can be efficiently prevented from penetrating into a print medium even when the inkjet printing is performed to the print medium having a hydrophilic porous surface.
According to the solvent ink containing the penetration inhibitor of the present invention, when inkjet printing is performed to a plate member for offset printing, the penetration of ink into the plate member is prevented so that the amount of an ink coating formed on the print surface of the plate member is increased. Accordingly, an offset printing plate with the ink coating having sufficient water resistance and water repellency can be obtained. When the offset printing plate is used for offset printing, sufficient adhesion of ink for offset printing relative to the offset printing plate can be obtained. Accordingly, the offset printing plate has excellent plate life.